Custom help message when using argh

Help messages generated from argh is nearly useless and very hard to
customize. Fork argh and disable all code for generating help messages.

Use a closure to print the help message when handling EarlyExit.

native/src/base/misc.rs

@@ -382,20 +382,21 @@ pub fn map_args<'a>(argc: i32, argv: *const *const c_char) -> Result<Vec<&'a Utf
 }
 
 pub trait EarlyExitExt<T> {
-    fn early_exit(self) -> T;
+    fn on_early_exit<F: FnOnce()>(self, print_help_msg: F) -> T;
 }
 
 impl<T> EarlyExitExt<T> for Result<T, EarlyExit> {
-    fn early_exit(self) -> T {
+    fn on_early_exit<F: FnOnce()>(self, print_help_msg: F) -> T {
         match self {
             Ok(t) => t,
             Err(EarlyExit { output, status }) => match status {
                 Ok(_) => {
-                    eprintln!("{}", output);
+                    print_help_msg();
                     exit(0)
                 }
                 Err(_) => {
                     eprintln!("{}", output);
+                    print_help_msg();
                     exit(1)
                 }
             },